Copolymers with amorphous blocks

After a brief recall of the methods of synthesis of block copolymers, we shall describe the principal types of organized structures, which have been observed in block copolymers both in mesomorphic and dry states. Then we shall examine the structure and properties of the most important block copolymers dividing them in three categories copolymers with amorphous blocks, copolymers with amorphous and crystallizable blocks, copolymers with blocks presenting biological interest. However, in this review, only such properties will be taken into account that are related to the microdomain structure of block copolymers. 

Scheme 2 Various donor and acceptor monomers can be combined to obtain block copolymers with amorphous or crystalline segments. In the left box, the polymerizable monomers are shown. On the right, the architectures of the resulting two main classes of D-A block copolymers are depicted amorphous-crystalline and crystalline-crystalline block copolymers...

Poly[styrene-b/ock-2-(cholesteryloxy-carbonyloxy)ethyl methacrylate] (PS -PChEMA) copolymers and similar diblock copolymers with amorphous butadiene (PB-PChEMA) [204] and n-butylmeth-acrylate (PBMA-PChEMA) [204,210] blocks were synthesized by a route analogous to that shown in Scheme 16, except that the nonmesogenic block was polymerized first. For example, styrene was polymerized first in THE at -78 °C using 3-BuLi as the initiator (Scheme 26). Diblock... 

Copolymers with amorphous A block and liquid crystalline B block have been synthesized. The hydroboration of polybutadiene or butadiene styrene block copolymer with 9-BBN yields the intermediate, which on oxidation, followed by esterification with cholesteryl chloroformate, leads to the formation [4] of the said polymer. 

In the field of amorphous, linear, binary block copolymers a lot of work has been done and extensively reviewed [1,2,5,92-97]. Among the binary, linear, block copolymers the diblock copolymers have been studied in great detail. They can be considered as model systems for more complicated block copolymers, like block copolymers with more than two components, or block copolymers with other block distributions. Here we will address experimental work in the field of their phase behavior and mention only some theoretical work in the following. For a detailed theoretical description see Chapter 5. 

So far we discussed systems with amorphous block copolymers only. A second level of self-assembly is the formation of liquid crystals or crystals within microdomains of block copolymers. 

Figure 16.15 TEM images for bulk state morphologies of PS- -PFS (a-c), PFS- -PMMA (d) and PMMA- -PFS-Z -PS-Z -PFS- -PMMA (e-f) (PFS = poly(ferrocenylethylmethylsilane) in (a)-(c) and the dimethyl analog in (d)-(f). ((a)-(c) Reprinted with permission from D.A Rider, K.A. Cavicchi, K.N. Power-Billard et al, Diblock copolymers with amorphous atactic polyferrocenylsilane blocks Synthesis, characterization, and self-assembly of polystyrene-block-poly(ferrocenylethylmethylsilane) in the bulk state, Macromolecules, 38, 6931, 2005. 2005 American Chemical Society, (d) Reprinted with permission from C. Kloninger and M. Rehahn, Bicontinuous gyroidic morphologies in ferrocenyldi-methylsilane-b-methyl methacrylate diblock copolymer blends, Macromolecules, 37, 8319, 2004. 2004 American Chemical Society, (e)-(f) Reproduced with permission from U. Datta and M. Rehahn, Synthesis and self-assembly of styrene-[l]dimethylsilaferrocenophane-methyl methacrylate penta-block copolymers, Molecular Rapid Communications, 2004,25,1615. Wiley-VCH Verlag GmbH Co. KGaA.)...

Gwyther, 1. and Manners, 1. (2009) Diblock copolymers with amorphous, high glass transition temperature, organometallic block synthesis, characterisation and self-assembly of polystyiene-i -poly(ferrocenylisopropyl-methylsilane) in the bulk state. Polymer 50, 5384—5389... 

Sakurai K., MacKnight W. J., Lohse D. J., Schulz D. N., and Sissano J. A. (1994) Blends of amorphous-crystalline block copolymers with amorphous homopolymers. 2. Synthesis and characterization of poly(ethylene-propylene) diblock copolymer and crystallization kinetics for the blend with atactic polypropylene. Macromolecules 27 4941-4951. 

By block copolymerisation so that one component of the block copolymer has a Tg well below the expected service temperature range (e.g polypropylene with small blocks of polyethylene or preferably polypropylene with small amorphous blocks of ethylene-propylene copolymer). 

Among the different pressure sensitive adhesives, acrylates are unique because they are one of the few materials that can be synthesized to be inherently tacky. Indeed, polyvinylethers, some amorphous polyolefins, and some ethylene-vinyl acetate copolymers are the only other polymers that share this unique property. Because of the access to a wide range of commercial monomers, their relatively low cost, and their ease of polymerization, acrylates have become the dominant single component pressure sensitive adhesive materials used in the industry. Other PSAs, such as those based on natural rubber or synthetic block copolymers with rubbery midblock require compounding of the elastomer with low molecular weight additives such as tackifiers, oils, and/or plasticizers. The absence of these low molecular weight additives can have some desirable advantages, such as ... 

Of the amorphous block copolymers, styrenic block copolymers are the vast majority. These are synthesized anionically in solution, with butyl lithium commonly employed as the initiator [4]. There are three processes for this polymerization ... 

Polystyrene homopolymer produced by free radical initiators is highly amorphous (Tg = 100°C). The general purpose rubber (SBR), a block copolymer with 75% butadiene, is produced by anionic polymerization. 

Hedrick et al. reported imide aryl ether ketone segmented block copolymers.228 The block copolymers were prepared via a two-step process. Both a bisphenol-A-based amorphous block and a semicrystalline block were prepared from a soluble and amorphous ketimine precursor. The blocks of poly(arylene ether ether ketone) oligomers with Mn range of 6000-12,000 g/mol were coreacted with 4,4,-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester diacyl chloride in NMP in the presence of A - me thy 1 morphi 1 i nc. Clear films with high moduli by solution casting and followed by curing were obtained. Multiphase morphologies were observed in both cases. 

Blend formulations, with amorphous polyarylates, 47-48 Block copolyesters, 18 Block copolymers, 6, 20... 

Abstract This chapter gives an overview of the research on the self-assembly of amorphous block copolymers at different levels of hierarchy. Besides the influence of composition and topology on the morphologies of block copolymers with linear, cyclic and branched topologies blends of block copolymers with low molecular weight components, other polymers or block copolymers and nanoparticles will also be presented. 

---